Position sensors, such as brushes, slip rings, or wire conductors, often employ contacts to indicate the position of a movable member. The elimination of contacts is desirable and can reduce electrical noise and disturbances caused by sliding electric contact. The contactless sensors maintain a gap between the sensor and a target structure, which can be challenging to maintain the sensing range in the presence of such a physical gap.
Examples of contactless sensors include capacitance-based position sensors, laser-based position sensors, eddy-current sensing position sensors, and linear displacement transducer-based position sensors. While each type of position sensor has its advantages, each type of the sensor may be best suited for a particular application. For example, the size of capacitors can make the sensor impractical when the position sensor must be small in size. The optical sensor can fail in the presence of dirt or grease. Magnetic sensors require precision housings and mechanical assembly to avoid errors caused by magnet or sensor misalignment, which can be difficult in some applications. In addition, in some applications, the size of the gap between the sensor and the target structure can change with time, and the location of the target structure can cause problems to the accuracy of some linear position sensors.
Accordingly, there is a need for a contactless sensor for determining a presence and/or relative position of a target structure arranged at a different distance from the sensor.